How do I know what part I need?

[Izman1000]

I have the age-old Porsche window issue... My driver's side window goes all the way up, but then drops down a quarter of an inch and won't go back up to seal with the top.

I've heard that this can be the regulator or the micro-switch (and I believe there are several of these switches). My question is, how do I know which part is making my window have the issue?

I'd rather not (and can't afford) to replace all the parts if there is a way to narrow it down to the bad component.

Thanks